Reverse shoulder prosthesis

1. An implant assembly for reverse shoulder arthroplasty, the assembly comprising:

a humeral component having a stem portion and a neck portion, the stem portion being configured for fixation to a humerus of a patient, and the neck portion being angularly oriented relative to the stem portion;

an adaptor fixed to the neck portion of the humeral component; and

a glenosphere bearing component coupled to the adaptor, the glenosphere bearing component having a first bearing surface and a second bearing surface opposite the first bearing surface;

wherein the first bearing surface of the glenosphere bearing component interfaces with an articulating surface of the adaptor to allow the adaptor and humeral component to rotate relative to the glenosphere bearing component about a rotational axis of the glenosphere bearing component;

wherein the adaptor and the glenosphere bearing component form a locking mechanism that prevents the adaptor from decoupling from the glenosphere bearing component while allowing the adaptor to remain rotatable relative to the glenosphere bearing component after the implant assembly is implanted in the patient; and

wherein the second bearing surface of the glenosphere bearing component is configured to interface with a glenosphere component to allow the glenosphere bearing component to articulate relative to the glenosphere component;

wherein the adaptor is configured to permit eccentric rotation of the adaptor and humeral component around the rotational axis relative to the glenosphere bearing component.

2. The implant assembly of claim 1 , wherein the glenosphere bearing component comprises a first coupling member matingly engaged with a second coupling member of the adaptor.

3. The implant assembly of claim 2 , wherein the first coupling member comprises a shaft extending from the first bearing surface, and the second coupling member comprises a recess in the adaptor configured to receive the shaft.

4. The implant assembly of claim 2 , wherein the first and the second coupling members are aligned with the rotational axis of the glenosphere bearing component.

5. The implant assembly of claim 4 , wherein a geometric center of the first bearing surface has a radial offset relative to the rotational axis.

6. The implant assembly of claim 2 , wherein the locking mechanism comprises a tongue-and-groove joint between the adaptor and the glenosphere bearing component so as to allow rotational movement of the glenosphere bearing component relative to the adaptor but resist axial displacement of the adaptor from the glenosphere bearing component.

7. The implant assembly of claim 2 wherein the first coupling member comprises a shank member extending outwardly from the first bearing surface and a keel member angularly extending from the shank member.

8. The implant assembly of claim 7 , wherein the second coupling member comprises a channel and a chamber connected to the channel, wherein the shank is positioned in the channel and the keel is angularly moveable within the chamber.

9. The implant assembly of claim 8 , wherein the chamber has a first angular boundary and a second angular boundary, and the angular movement of the keel within the chamber is limited by the first and second angular boundaries.

10. The implant assembly of claim 9 , wherein the first angular boundary and the second angular boundary defines a circular sector having an angle from about 30° to about 150°.

11. The implant assembly of claim 2 , further comprising a first limiter and a second limiter, the first and second limiters being configured to limit rotational movement of the adaptor relative to the glenosphere bearing component.

12. The implant assembly of claim 11 , wherein the first limiter is angularly spaced apart from the second limiter from about 30° to about 150° with respect to the rotational axis of the glenosphere bearing component.

13. The implant assembly of claim 11 , wherein the first and second limiters are disposed on the glenosphere bearing component.

14. The implant assembly of claim 11 , further comprising a curved groove located on the first bearing surface of the glenosphere bearing component and a tab extending outwardly from the articulating surface of the adaptor, the tab being configured to be received in and moveable within the curved groove, wherein a first and second ends of the groove define the respective first and second limiters.

15. The implant assembly of claim 1 , further comprising the glenosphere component, wherein the glenosphere component comprises a base configured for fixation to a glenoid fossa of scapula of the patient and a convex surface that articulates against the second bearing surface of the glenosphere bearing component, wherein the second bearing surface is concave.

16. The implant assembly of claim 1 , wherein the articulating surface of the adaptor and the first bearing surface of the glenosphere bearing component form a planar interface.

17. The implant assembly of claim 1 , wherein the articulating surface of the adaptor and the first bearing surface of the glenosphere bearing component form a non-planar interface.

18. The implant assembly of claim 1 , wherein the neck portion of the humeral component comprises a neck recess and the adaptor comprises a projection opposite the articulating surface of the adaptor, wherein the projection of the adaptor is fixed to the neck recess.

19. The implant assembly of claim 1 , wherein the adaptor comprises a metallic material and the glenosphere bearing component comprises a polymeric material.